Method and apparatus for regenerating an iron-based fischer-tropsch catalyst

ABSTRACT

Solvent extraction is used to remove wax and contaminants from an iron-based Fischer-Tropsch catalyst in a natural circulation continuous-flow system. The wax-free catalyst is then subjected to controlled oxidation to convert the iron to its initial oxidized state, Fe 2 O 3 . Reactivation of the oxide catalyst precursor is carried out by addition of synthesis gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims the benefitunder 35 U.S.C. §121 of U.S. patent application Ser. No. 11/874,661,which is a divisional of U.S. patent application Ser. No. 11/005,873,which claims priority to U.S. Pat. No. 6,838,487, the disclosures ofeach of which are hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

FIELD OF INVENTION

The present invention relates to the production of liquids and waxesfrom synthesis gas using the Fischer-Tropsch (FT) process, and moreparticularly to regenerating an iron-based FT catalyst that has becomedeactivated due to buildup of contaminants on the surface of thecatalyst.

BACKGROUND OF THE INVENTION

The low costs associated with iron-based FT catalysts have heretoforebeen a major factor in the lack of development of methods forregenerating these catalysts. However, increasing concerns over disposalof industrial wastes in landfills from both economic and environmentalstandpoints have created a need for improved methods for recycling spentcatalysts—even for the low-cost catalysts. When a catalyst is employedin a slurry reactor, disposal of spent catalyst can be challenging. Somemethods have been proposed which rejuvenate iron-based catalysts for ashort period of time, but an economical method is needed for returningthe catalyst back to its initial oxide state without causing attritionor sintering of the catalyst.

Moreover, to regenerate such iron-based catalysts, several areas ofconcern must be addressed. The oxidation step must be controlled toprevent overheating and sintering of the catalyst. Usually, thetemperature during oxidation is controlled by limiting the percentage ofoxygen present in the gases used for oxidation. However, when limitedoxygen is available during oxidation, the presence of wax with thecatalyst can cause carbon formation. Therefore, efficient and completewax removal is a key to successful catalyst regeneration.

Further, de-waxing must be carried out in a continuous flow systemwithout subjecting the catalyst to mechanical stresses, which can causethe catalyst particles to break apart.

The present invention provides an economical method of returning aniron-based FT catalyst back to its initial oxide state without causingcatalyst attrition or sintering, thereby allowing the regeneration of acatalyst that has become deactivated due to buildup of contaminants onits surface.

DESCRIPTION OF THE PRIOR ART

There are several potential mechanisms of deterioration of iron-based FTcatalysts. The primary mechanisms suspected of causing deteriorationinclude composition change of the catalyst, crystallite growth due tosintering, and contamination of active sites by a carbon layer. Inaddition, iron-based catalysts undergo a shift in selectivity toward theproduction of lighter products with time on stream as well as areduction in activity.

Thus, it is well-known that build up or growth on the surface of thecatalyst tends to inhibit the activity of the catalyst. U.S. Pat. No.5,397,806 issued to Soled et al. states, “In virtually any catalyticprocess, catalyst activity decreases as run length increases due to avariety of factors: deposition of coke or carbon on the catalyst as aresult of cracking, hydrogenolysis, or polymerization, buildup ofpoisons in the feed such as sulfur or nitrogen compounds, etc. Inhydrocarbon synthesis reactions, carbon tends to build up or grow (bycomplex polymerization mechanisms) on the surface of the catalyst,thereby shielding the catalytic metals from the reactants. Activitydecreases and at some pre-set level of activity (as defined byconversion or selectivity or both), the process becomes sufficientlyuneconomical to continue and the catalyst is either replaced orregenerated. In either case, downtime results and in the former,significantly increased catalyst costs are incurred.”

U.S. Pat. No. 2,620,347 to Rottig describes an iron-based catalyst, anoperating regime, and a solvent extraction procedure to produce acatalyst which converts about 70% of the water gas (H₂:CO=1) tosubstantial amounts of hydrocarbon products boiling above 300° C. One ofthe catalysts described therein was prepared by soda precipitation ofiron and copper nitrates, washed, impregnated with potassium phosphateand dried. The catalyst precursor was then reduced in hydrogen at 230°C. The reduced catalyst was treated with water gas at a temperature of150° C. at atmospheric pressure. Over a period of 48 hours, thetemperature was increased to 190° C. at which point the carbon monoxideplus hydrogen conversion reached 85%. During the next 48 hours, thehydrogen conversion dropped to 27% by reason of adsorption of paraffinmaterial onto the catalyst. The exhausted catalyst was then thoroughlyextracted at a temperature between 170° C. and 195° C. with five timesits volume of hydrogenated diesel oil fraction having a boiling pointbetween 220-260° C. This regenerated catalyst was again subjected towater gas at 150° C., as before. Here, the carbon monoxide plus hydrogenconversion was about 45%. After 72 hours, the conversion dropped to 40%by reason of adsorption of paraffin material onto the catalyst. Thesynthesis and regeneration cycles were repeated several times until thecarbon monoxide plus hydrogen conversion stabilized at about 70%.Rottig's catalyst had a useful life of several thousand hours with anaverage conversion rate of about 70%. During this period, regenerativeextractions were carried out every 5-6 days initially and every 10-14days subsequently.

U.S. Pat. No. 2,632,015 to Kratzer describes a novel regenerationprocess using ethanol. The procedure is directed toward removing carbonfrom an iron catalyst which has operated at high temperatures in afluidized bed Fischer-Tropsch reactor. The carbon on the catalyst, orperhaps the carbon in iron carbide, reacts with ethanol in a fluid bedreactor at a pressure between 150 psi and 600 psi and a temperaturebetween 660° F. and 680° F. to produce acetone. The ethanol is separatedfrom the acetone and recycled to the regenerator. Additional treatmentof the catalyst is described whereby hydrogen, or a mixture of hydrogenand steam, is introduced into the fluidized bed at a temperature between700° F. and 900° F. for a period of time between eight and fifteenhours.

U.S. Pat. No. 6,121,179, McBrayer, Jr. et al. describes a process forremoving organic contaminants from adsorbent materials usingsupercritical water. The organic contaminants are destroyed in a secondstage by oxidation.

U.S. Pat. Nos. 6,114,399 and 6,217,830, both to Roberts and Kilpatrick,disclose methods and apparatus, respectively, for using supercriticalorganic solvents to effect wax/catalyst separation for a FT slurryreactor. In these patents, the solvent and wax/catalyst slurry are mixedto dissolve wax in the solvent, and the wax-laden solvent is separatedfrom the catalyst, which is returned to the FT reactor. The solvent andwax are separated via one or more stages of flash separation. Therecovered solvent is recycled to the mixer and the wax is collected asproduct. The procedures described in these patents, however, do notprovide a wax- and contaminant-free catalyst.

U.S. Pat. No. 2,487,867 to Griffin, Jr. describes a process forpurifying catalyst particles used in a fluidized bed FT reactor. Aslipstream of catalyst and hydrogen is fed to a hydrogenation reactorwherein waxy and oily deposits are destructively hydrogenated to formvolatile products, and to lower the molecular weight and viscosity ofthe oily material remaining on the catalyst. The catalyst is then fed toa second vessel for washing with a solvent. After drying, the catalystis returned to the fluidized bed FT reactor. For an iron-based catalyst,Griffin, Jr. recommends that the hydrogenator be operated at atemperature of 450° F. to 750° F., and at a pressure of 25-350 psig. Thesolvent can be naphtha, gasoline, or liquefied petroleum gases.

U.S. Pat. No. 2,533,072 to Voorhies, Jr. discloses a hydrogen treatmentmethod of decarbonizing a FT catalyst used in a fluidized bed reactor.Since the decarbonizer must operate at a higher temperature (1000-1200°F.) than the FT reactor (600-750° F.), sufficient CO is supplied alongwith the hydrogen, which is fed to the decarbonizer to provide anexothermic reaction to heat the decarbonizer to the requisitetemperature. Sufficient carbon is removed from the catalyst to maintaina carbon content of the catalyst in the FT reactor of below 20 percentby weight.

U.S. Pat. No. 5,817,701, Leviness and Mitchell, describes a process forrejuvenating a partially deactivated catalyst used in a three-phase FTbubble column reactor (BCR). Synthesis gas flow into the FT reactor isinterrupted and replaced with a hydrogen rich rejuvenating gas. Thisrejuvenating gas is recycled back to the reactor after water scrubbingremoves deactivating species. The rejuvenating gas was specified tocontain at most 5-10% CO and to have a H₂:CO ratio of at least 3-5. Inone embodiment of the invention, CO₂ was present in the rejuvenating gasin sufficient amounts to suppress the water gas shift reaction.

In U.S. Pat. No. 6,162,754, Maretto et al. describe the use of a drafttube situated inside a FT slurry BCR for regenerating catalyst. Catalystflows from the top of the draft tube downward between the draft tube andreactor wall. A regenerating gas, preferably hydrogen, is introducedinto this annular region for contact with the catalyst. After a periodof time, the hydrogen flow is stopped and circulation of slurry from thedraft tube into the annular region resumes, thereby displacing theregenerated catalyst into the draft tube where the FT reaction takesplace. This sequence is repeated without having to interrupt the FTreaction.

In U.S. Pat. No. 6,022,755, Kinnari and Schanke describe a novel methodof regenerating a catalyst used in a slurry BCR. In order to provide ahydrogen-rich gas for regeneration, the space velocity is lowered to alevel wherein the outlet gas composition is low in carbon monoxide andhigh in hydrogen. During this mode of operation, the CO conversion ishigh, the H₂:CO ratio is high, the CO₂ selectivity is high, and the C5+selectivity is low. The resulting effect of the new reaction mode is aregenerative gas mixture. Therefore, it is not necessary to change thesynthesis gas composition for regeneration.

When an iron-based catalyst has deactivated irreversibly, however,oxidation may be the only way to remove the deactivating species andallow salvaging of the catalyst. Under these circumstances,re-activating the resulting iron oxide (hematite) is necessary. Thedifficulty in oxidizing the precipitated iron catalyst is, however,preventing overheating and sintering of the catalyst.

U.S. Pat. No. 2,661,338 to Lanning teaches a procedure for regeneratingan iron-based FT catalyst used in a fluidized bed reactor. In Lanning,carbonaceous deposits are oxidized in a combustion reactor and ironoxide is melted as it falls through a combustion zone. Solid iron oxideparticles are formed as the droplets move down through a cooling zone ofthe reactor. Agglomerated particles are broken up by grinding. The fusediron particles are reduced in hydrogen and returned to the FT reactor.This method, however, is not applicable to a precipitated iron catalyst.

Kalbel and Ralek [Catal. Rev.-Sci. Eng., 21(2), 246-247 (1980)] refer tothe successful regeneration of a precipitated iron catalyst used in aslurry BCR by controlled oxidation. However, no details were revealed.

Publication No. US 200210183403 A1 to Huang et al., which published Dec.5, 2002, discloses a process for regenerating a slurry FT catalyst,which involves de-waxing and drying the catalyst sufficiently to producea free-flowing catalyst powder that is fluidizable; fluidizing thecatalyst powder; treating the catalyst powder with an oxygen treatment;reducing the catalyst powder with a reducing gas to form a reducedcatalyst powder; and mixing the reduced catalyst powder withhydrocarbons to form a regenerated, slurry catalyst. Although theprocess is similar to that of the present invention, Huang et al. doesnot teach catalyst regeneration involving the apparatus of the presentinvention.

Apparatus

Several patents describe various means for integrating catalystrejuvenation or regeneration steps with a FT slurry bubble columnreactor.

Illustrative of such prior art are the following patents: U.S. Pat. No.5,260,239 issued to Stephen J. Hsia, titled “External CatalystRejuvenation System for the Hydrocarbon Synthesis Process”; U.S. Pat.No. 5,268,344 issued to Pedrick et al., titled “Draft Tube for CatalystRejuvenation and Distribution”; U.S. Pat. No. 5,288,673 issued toBehrmann et al., titled “Temperature Control in Draft Tubes for CatalystRejuvenation”; U.S. Pat. No. 5,811,363 issued to Leviness et al., titled“Catalyst Rejuvenation in Hydrocarbon Synthesis Slurry with ReducedSlurry Recontamination”; U.S. Pat. No. 5,811,468 issued to Chang et al.,titled “Combination Gas Disengaging Downcomer-Rejuvenation Tube forIn-situ Slurry Catalyst Rejuvenation (LAW541)”; U.S. Pat. No. 5,821,270issued to Chang et al., titled “Slurry Hydrocarbon Synthesis Processwith Multistage Catalyst Rejuvenation”; and U.S. Pat. No. 6,201,030issued to Gary L. Beer, titled “Process and Apparatus for Regenerating aParticulate Catalyst.”

SUMMARY OF THE INVENTION

In accordance with the present invention, catalyst in a slurry isremoved from a FT reactor, de-waxed and subjected to controlledoxidation to restore the catalyst to its original oxidized andunactivated state. The following steps are carried out: 1) a slurrycomprising wax and catalyst removed from a Fischer-Tropsch reactor isplaced into a vessel and heated to about 120° C. (the melting point ofwax) or higher; 2) a gas is introduced into the bottom of the vesselthereby producing a three-phase bubble column; 3) degassed slurry fromthe vessel is allowed to flow under natural circulation through acatalyst settling vessel back to the bubble column vessel, therebyreturning slurry containing deactivated catalyst to the bubble columnvessel; 4) extraction solvent is added to the bubble column vessel tomaintain slurry level as catalyst-free wax and solvent are removed fromthe catalyst settling vessel; 5) catalyst-free wax and solvent which areremoved from the catalyst settling vessel are fed to a flash vessel forseparation of wax and solvent; 6) separated wax is sent to a waxrecovery, or wax hydrocracking, system; 7) recovered solvent from theflash vessel is returned to the bubble column vessel along with solventwhich is recovered from separation of bubble column overhead gas; 8) thede-waxed catalyst in the bubble column vessel is separated from thesolvent and subjected to controlled oxidation; 9) after purging thebubble column vessel with inert gas, the oxidized catalyst precursor inthe bubble column vessel is mixed with wax, diesel or other suitableslurry medium to form a three-phase slurry comprised of catalystprecursor, slurry medium, and inert gas; 10) the three-phase slurry istreated with synthesis gas in a slurry mode to produce an activecatalyst containing iron carbides; and 11) the slurry containing theactivated catalyst is removed from the bubble column vessel.

One aspect of the present invention is that wax removal and recoveryfrom a deactivated catalyst is nearly 100%.

Another aspect of the present method is that a low concentration ofcatalyst in a slurry can be accommodated. Wax in the slurry is removedfrom the system as solvent is added to replace the removed wax, wherebyslurry levels are maintained.

Yet another aspect of the present invention is that the catalyst is notsubjected to pumps or other mechanical devices which could causeattrition of the catalyst particles.

Yet another aspect of the present invention is that the process isoperated separate from the FT reactor. Therefore, the extraction processcan be operated under optimal pressures and temperatures, e.g., at ornear supercritical conditions of the solvent. For example, the criticaltemperature and pressure for normal hexane are 507.9 K and 3034 KParespectively.

It is an aspect of the present invention that the rate of removal ofclarified solvent and wax from the dynamic settler can be adjusted froma low rate initially when primarily high-viscosity wax is being removed,to a high rate when primarily low-viscosity solvent is being removed.

Another aspect of the present invention is that the same apparatus canbe used to carry out all of the steps from wax extraction to catalystactivation.

Other aspects of this invention will be apparent upon reading thefollowing description and appended claims, reference being made to theaccompanying drawings which form a part of this specification. In thedrawings, like reference characters designate corresponding parts in theseveral views.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a solvent extraction apparatuscomprising a slurry bubble column for intimately mixing a solvent and aslurry, a dynamic settler device for separating catalyst-free solventand wax (described in U.S. Pat. Nos. 6,068,760 and incorporated hereinby reference), a flash distillation vessel for separating solvent fromwax, and other equipment useful for condensing and recovering solvent.After wax has been extracted from the catalyst, the catalyst can beoxidized and re-activated using the same apparatus.

FIG. 2 is a graphical depiction of extractor liquid composition plottedagainst time using the parameters established in Example 1.

FIG. 3 is a graphical depiction of hexane flowrate in extractor overheadgases plotted against time using the parameters established in Example1.

FIG. 4 is a graphical depiction of catalyst settling vessel outlet waxand hexane flowrates plotted against time using the parametersestablished in Example 1.

FIG. 5 is a graphical depiction of hexane flowrates from a flashevaporator plotted against time using the parameters established inExample 1.

Before explaining the disclosed embodiments of the present invention indetail, it is to be understood that the invention is not limited in itsapplication to the details of the particular arrangements shown, sincethe invention is capable of other embodiments. Also, the terminologyused herein is for the purpose of description and not of limitation.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

The slurry removed from the FT reactor, and subjected to the extractionprocess described herein below, is a mixture of catalyst particlescomprised of iron carbides, mainly Fe₅C₂ and Fe_(2.2)C, iron oxide inthe form of magnetite, Fe₃O₄, and hydrocarbon molecules, primarilyparaffins and olefins with carbon numbers ranging from about 15 to 100.A small amount of oxygenates may be present—mainly alcohols. Theparticle size of the catalyst particles may range from 1 to 100 μm.

The extraction of wax from the catalyst particles requires intimatemixing of the solvent with the slurry and catalyst particles. Efficientmixing can be effected by bubbling an inert gas up through the slurry ina bubble column reactor. A bubble column reactor useful for extractionin the instant case can be similar in design to the bubble columnreactor used in a Fischer-Tropsch process described in U.S. Pat. No.5,620,670 which is incorporated herein by reference. However, theoperating parameters for extraction can be significantly different fromthe parameters used for a FT reaction. The pressure in the extractor canbe selected to limit the amount of solvent leaving the extractor withthe inert gas. The temperature of the extractor must be above themelting point of the wax, i.e., approximately 100° C. Superficialvelocity, defined as the velocity that the inert gas would have in theextractor without slurry at the temperature and pressure of theextractor, is a key parameter. To achieve good mixing and preventcatalyst particle settling, the superficial velocity must be above about2.5 cm/s.

The higher the extractor pressure, the larger the amount of inert gasflow required to achieve a desired superficial velocity. On the otherhand, higher pressures reduce the amount of solvent in the overheadgases. In some instances it may be desirable to use desulfurized naturalgas as the inert gas since this gas can be flared readily.

As the bulk wax is removed and replaced with solvent, it may benecessary to increase the pressure and/or temperature of the solvent toimprove the effectiveness of removing wax from the pores of the catalystparticles and to reduce the amount of solvent carried overhead with theinert gas.

Removal of catalyst-free wax from the system is accomplished using adynamic settler such as the one described in U.S. Pat. No. 6,068,760which is incorporated herein by reference. The dynamic settler enablesthe removal of essentially catalyst-free wax from the system. The degreeof liquid/catalyst separation is dependent upon the viscosity of theliquid and upon the upward velocity of the liquid in the settler. Asufficiently low upward velocity in the settler can result in acatalyst-free liquid removed from the settler. Unlike the situationwherein the settler must be designed to accommodate a fixed flowrate ofwax from the settler when it is used as the primary wax/catalystseparation means on a FT reactor, the current application permits theflowrate to be varied according to the properties of the liquid beingremoved. For example, initially when the liquid being removed isprimarily wax, the flowrate can be low to prevent entraining catalystparticles. As the extraction progresses, the flowrate can be increasedsince the liquid will contain primarily solvent possessing a lowviscosity. To determine whether the catalyst has been fully dewaxed, asample of solvent can be chilled to see whether wax crystals precipitatefrom the solvent.

The liquid mixture of wax and solvent from the settler is separated byflash evaporation, wherein the pressure of the liquid is reduced acrossa valve causing most of the solvent to vaporize and flow overhead fromthe flash vessel for condensing and recovery. The liquid wax isrecovered from the bottom of the vessel. Since the temperature of theslurry in the extractor and in the settler may be too low for effectivewax/solvent separation in the flash evaporator, it may be advantageousto increase the temperature of the wax/solvent mixture after the settlerand before the flash evaporator. A higher temperature in the flashevaporator will lower the amount of solvent contained in the wax stream.

After wax has been removed from the catalyst, the liquid in theextractor will be wax-free solvent. This solvent must be removed fromthe extractor to leave a dry catalyst powder. Removal of the solventfrom the extractor is accomplished by gradually lowering the extractorpressure, thereby causing the solvent to vaporize and leave in theoverhead gases. The solvent is condensed and placed in a storage tank.By maintaining inert gas flow during the solvent vaporization step, thecatalyst will not agglomerate.

The dry catalyst powder is ready for oxidation. The oxidation step burnsoff carbon deposits on the catalyst surface and produces carbon dioxideand possibly carbon monoxide. Oxidation can be carried out in the samevessel used for wax extraction. Air is added to the inert gas to producea mixture containing about 2% by volume of oxygen. By preventing thecatalyst bed temperature from exceeding about 220° C., sintering isavoided. Completion of oxidation can be determined by the lack of CO orCO₂ in the tail gases. The oxidation step can be carried out at apressure slightly above atmospheric pressure. The flowrate of theoxidizing gas mixture should give a superficial velocity of about 2.5cm/s.

It has been found that, in some cases, the alkali content of ironcatalysts that have undergone the extraction and oxidation steps wassignificantly lower than that of fresh catalyst. Re-alkalization can becarried out in the same apparatus as was used for extraction andoxidation. Solvent containing the alkali promoter can be added to thevessel containing the oxidized catalyst. Inert gas bubbling through theslurry provides good mixing. The solvent can be evaporated from thereactor by raising the temperature until a dry catalyst powder isproduced. Again, maintaining flow of inert gas during the drying stepwill prevent agglomeration of the catalyst particles.

The final step in catalyst regeneration is treating the catalyst withsynthesis gas to form iron carbides. This activation step can be carriedout in the same vessel in a fluidized bed mode or in a liquid slurrymode; however better temperature control can be achieved with a slurry.The slurry liquid medium is added to the catalyst powder, and inert gasis bubbled through the slurry at a superficial velocity greater than 2.5cm/s. The pressure, temperature and syngas composition used in theactivation step can be the same as those used during the initialactivation of the fresh catalyst.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIG. 1, an apparatus according to an embodiment of thepresent disclosure comprises a slurry bubble column extractor 3, whichserves to provide intimate mixing of the slurry 2 comprised of wax,catalyst, solvent and gas. Inert gas 4 is fed to gas preheater 6 throughgas conduit 5 prior to being fed to the gas distributor 8 throughpreheated gas conduit 7. In the extraction step, gas 4 is the lift gasfor circulating slurry 2 through to the dynamic settler 12 and itprovides the energy for mixing slurry 2 in the bubble column extractor3. The bubble column extractor 3 is equipped with heating/coolingapparatus 1 to maintain slurry 2 at the desired operating temperature.This device is offered by way of example and not limitation.Heating/cooling apparatus 1 can be a steam jacket, electrical heatingelements, an internal tube bundle or other suitable means. Bubble columnextractor 3 is equipped with a downward sloping slurry overflow conduit9 which is connected to gas disengaging conduit 11, through valve 10.Gas disengaging conduit 11 unites with degassed slurry conduit 13 whichis situated vertically along the centerline of dynamic settler 12.

Degassed slurry conduit 13 extends approximately 80% of the length ofsettler 12 and delivers degassed catalyst-bearing slurry near a bottomoutlet of settler 12. The degassed slurry which exits conduit 13 flowsas a free jet into the slurry which surrounds conduit 13. Gas bubblesleaving the slurry flowing in conduit 9 are directed through gasdisengaging conduit 11 along with overhead gases from bubble columnextractor 3 via gas outlet conduit 21 to a cooling heat exchanger 23 viamixture conduit 22. Conduit 24 carries the cooled gas mixture to a firstseparator vessel 25. Degassed slurry flows from settler 12 back tovessel 3 via valve 16 and return conduit 15. Due to the difference indensities of the degassed slurry and the bubbly slurry in vessel 3, theslurry and bubbles in conduit 9 and the degassed slurry in conduits 13and 15 flow by natural circulation. Dynamic settler 12 is equipped withheating apparatus 14 to maintain the settler contents at a desiredtemperature. Initially, the clarified liquid removed from settler 12will be primarily wax, whereas at the end of extraction, the clarifiedliquid will be only solvent.

Catalyst-free liquid, or the wax/solvent mixture, is removed fromsettler 12 via clarified liquid conduit 38 located near the top ofsettler 12. Note that the clarified liquid flows upward in an annularregion surrounding degassed slurry conduit 13 opposite in direction tothe slurry flow issuing from conduit 13 and requires catalyst particlesto reverse directions. The wax/solvent mixture in clarified liquidconduit 38 contains dissolved gases and volatile solvent, which areseparated from the liquid wax in flash vessel 42 by dropping thepressure across valve 41. It is advantageous to heat the wax/solventmixture in heat exchanger 39 upstream of flash valve 41 to provide goodseparation of solvent in the vapor phase from wax in the liquid phase.Wax which collects at the bottom of flash vessel 42 is fed to collectiontank 59 through evaporator wax conduit 58 and valve 56 which is actuatedby liquid level controller 57 located at the bottom of flash vessel 42.Wax is pumped from collection tank 59 via tank wax conduit 60 by pump 61and sent to wax storage or processing via wax storage conduit 62. Thegaseous compounds in flash vessel 42 leave the top of vessel 42 viaevaporator gas conduit 43 and are cooled in heat exchanger 44. Thetwo-phase mixture leaving heat exchanger 44 flows through two-phasemixture conduit 45 into a second separator vessel 46. Liquids, primarilysolvent, collecting in the bottom of second separator 46 are fed tostorage tank 51 through separator vessel conduit 50 and valve 48actuated by level controller 49 located in at the bottom of secondseparator vessel 46. The overhead gases from bubble column extractor 3and gases in gas disengaging conduit 11 flow into gas outlet conduit 21.Mixture conduit 22 carries the gas mixture to cooling heat exchanger 23,whereby conduit 24 carries the cooled gas mixture to first separatorvessel 25. The overhead gases from first separator 25 are fed toback-pressure regulator 27 via separator overhead gas conduit 26. Thegases flowing through back-pressure regulator 27 in regulated gasconduit 28 are combined with gases flowing in separator overhead gasconduit 47 from second separator 46 and are sent to a flare 64 or otherdisposal means via disposal conduits 29, 34 and 63. A gas sample may beremoved from disposal conduit 29 via sample line 32 to determine whetheroxidation or catalyst activation, as discussed below, is complete.

In the case where the gases flowing in disposal conduit 29 are inert,combustible gas 30 can be added to inert gases present in gas conduit 31to produce a suitable gas for flaring 64. Alternatively, inert gascarried in disposal conduits 29 and 34 may be routed via return gasconduit 65 to pump 66 for reintroduction into bubble column vessel 3 bymeans of conduits 67, 5, and 7.

During catalyst activation, inert gas 4, a purge gas, is fed to vessel 3via conduit 5 to purge all oxygen from the system. Liquids, primarilysolvent, in the bottom of first separator vessel 25 are released fromseparator vessel 25 through valve 35, which is controlled by liquidlevel controller 36, into storage tank 51 via separator vessel conduit37. Liquids, primarily solvent, in the bottom of second vessel 46 arereleased from separator vessel 46 through valve 48, which is controlledby liquid level controller 49, into storage tank 51 via separator vesselconduit 48. Pump 53 pumps the primarily solvent liquids from storagevessel 51 into storage tank solvent return conduit 54 via solventconduit 52. Pump 53 increases the pressure to a level greater than thepressure in bubble column extractor 3. The liquid in storage tanksolvent return conduit 54 is fed to heat exchanger 20 whereby liquids(solvent) in storage tank solvent return conduit 54 are heated andbubble column extractor gases flowing in overhead gas conduit 19 arecooled. The heated liquids are fed to bubble column extractor 3 viaheated solvent return conduit 55. Since some solvent will be lost to theoverhead gases via disposal conduit 34 and to the wax stream via waxstorage conduit 62, makeup solvent 17 is added to extractor 3 throughmakeup solvent conduit 18 in order to maintain a constant slurry heightin extractor 3.

After completion of extraction, the temperature of the solvent inextractor 3 is lowered to about 90° C. by reducing the energy output ofheater 1. This lower temperature is desirable to prevent violentflashing of the solvent when the pressure is lowered. After theextractor temperature has reached the desired level, settler 12 isisolated from extractor 3 by closing valves 10 and 16. Back-pressureregulator 27 is used to reduce the pressure of extractor 3 to about 50psia. Under these conditions, the solvent evaporates, is condensed incooling heat exchanger 23, and is separated from fluidizing gases infirst separator vessel 25. Pump 53 is shut off and solvent from firstseparator 25 collects in storage tank 51 until the next extractioncycle. Evaporation of the solvent is continued until all of the solventhas been removed from extractor 3. Air 70 is added to inert gas 4 viaair conduit 71 to produce an oxidizing gas containing about 2% by volumeoxygen. The oxidizing gas is fed through gas conduit 5, heated to about220° C. in heat exchanger 6 and fed to extractor 3 via preheated gasconduit 7 through gas distributor 8. In embodiments, gas distributor 8comprises a sintered metal plate. The sintered metal plate can have amean pore diameter in the range of from about 0.2 μm and about 2 μm. Thetemperature of the fluidized catalyst bed in extractor vessel 3 iscontrolled to about 220° C. and maintained for sufficient time to returnthe iron in the catalyst to hematite, Fe₂O₃. Completion of oxidation isdetermined by absence of carbon dioxide and carbon monoxide in gassample 33 removed from disposal conduit 29 via sample line 32.Determination of the presence of carbon dioxide and/or carbon monoxidein gas sample 33 can be made using a gas chromatograph, infrareddetectors, or any other suitable means.

Prior to catalyst activation, inert gas 4, a purge gas, is fed to vessel3 via conduit 5 to purge all oxygen from the system. Wax, diesel orother appropriate slurry medium 72 is fed to bubble column vessel 3 viaslurry medium conduit 73 to form a three-phase slurry comprised ofcatalyst precursor, slurry medium and inert gas in bubble column vessel3. Activating gas 68 comprised of CO alone or CO combined with inert gasand H₂ is fed to preheater 6 via activating gas conduit 69 and gasconduit 5 and thence to vessel 3 via preheated gas conduit 7. Thetemperature and pressure are adjusted appropriately to cause formationof iron carbides. Progress of activation can be determined by analyzingtail gases 33 via sample line 32.

After completion of activation, activating gas 68 is shut off andreplaced by inert gas 4 to purge all combustible gases from thecatalyst-bearing slurry and reactor vessel 3 as determined bycomposition of tail gas 33. After purging and cooling the slurry toabout 150° C., the resultant slurry 76 can be removed safely fromreactor vessel 3 via product conduit 74 and valve 75. At this point,slurry 76 containing regenerated catalyst is ready for return to aFischer-Tropsch slurry reactor.

Example 1

Calculations were carried out using Rentech's in-house computer programsto determine the approximate performance of the extractor and flashevaporator. A single compound tritriacontane (C₃₃H₅₈) was used torepresent wax, and hexane was used as the solvent in the calculations.The inert gas was assumed to be nitrogen. The extractor parameters arelisted below:

Diameter 61 cm Height 400 cm Quantity of Wax 1.72 kg · mols Superficialvelocity of N₂ 2.5 cm/s N₂ flowrate 13.7 kg · mols/h Gas holdup 0.15Pressure 1.72 MPaa Temperature 125° C.

For the settler, it was assumed that initially the upward velocity wouldbe only 4 cm/h since the wax would hinder settling of the catalyst. Asthe composition changed in the settler to a higher percentage of hexane,the upward velocity was assumed to increase according to the formulaV=4+36*f, where f is the fraction of hexane in the liquid.

The parameters for the settler are as follows:

Diameter 91.4 cm Liquid upward velocity 4 cm/h for wax only Liquidupward velocity 40 cm/h for hexane only Pressure 1.72 MPaa Temperature125° C.

The flash evaporator parameters are:

Pressure 0.14 MPaa Temperature 204° C.

In the example, hexane is recovered from the overhead condenser and fromthe flash evaporator reheated and recycled to the extractor to maintainliquid inventory in the extractor. There is a gradual replacement of waxby hexane initially and a more rapid replacement as the hexane fractionincreases. This change in composition is shown in FIG. 2. According tothis example, the extraction of wax from the slurry using hexanerequires about 24 hours. Due to the stripping action of the nitrogen,hexane is carried overhead and recovered after condensing. The rate ofhexane removed in the overhead gases as a function of time is shown inFIG. 3. FIG. 4 is a plot of flowrates of hexane and wax removed from thesettler as a function of time. FIG. 5 is a plot of flowrates of liquidand vapor hexane from the flash evaporator according to the calculationsfor Example 1.

Example 1 is presented herein to show one embodiment of the inventionand should not be construed as a limitation of the invention. Differentgases, solvents, pressures and temperatures can be chosen by one skilledin the art to optimize the different steps of the invention. Solventsother than hexane such as hexene, heptane, heptene, tetrahydrofuran andFischer-Tropsch naphtha can be used. Also, the novel method of waxextraction described herein can be applied to any wax-ladenFischer-Tropsch catalyst, including cobalt and ruthenium.

Although the present invention has been described with reference to thedisclosed embodiments, numerous modifications and variations can be madeand still the result will come within the scope of the invention. Nolimitation with respect to the specific embodiments disclosed herein isintended or should be inferred.

1. An apparatus useful for separating a wax-free catalyst from anextraction solvent in a wax-free catalyst and solvent bearing solutionafter a wax extraction process and forming a dry catalyst powder, saidapparatus comprising: evaporation means functioning to vaporize saidextraction solvent for discharge in an overhead gas, thereby removingsaid extraction solvent from said evaporation means; condensing meansfunctioning to condense solvent present in the overhead gas; separationmeans functioning to separate said overhead gas from said condensedsolvent exiting the condensing means; and solvent storage meansfunctioning to store condensed solvent.
 2. The apparatus of claim 1further comprising solvent pumping means for pumping solvent to saidevaporation means for another extraction.
 3. The apparatus of claim 1,wherein said evaporation means further comprises a three phase bubblecolumn.
 4. The apparatus of claim 3 further comprising a gasdistribution means functioning to distribute the inert gas uniformlyacross a cross sectional area of said three phase bubble column.
 5. Theapparatus of claim 3, wherein the evaporation means used for solventevaporation is the same as the extraction vessel used for extracting waxduring the wax extraction process.
 6. The apparatus of claim 1, whereinsaid solvent evaporation means further comprises a temperature controlmeans functioning to maintain the wax-free catalyst and solvent bearingsolution at a desired temperature.
 7. An apparatus useful for oxidizingwax-free deactivated iron-based FT catalyst back to an original Fe₂O₃catalyst precursor state after a wax extraction process in an extractionvessel, said apparatus comprising: vessel means functioning to contactsaid deactivated wax-free catalyst with an oxidizing gas to form acatalyst bed; and heating means functioning to heat the vessel means,thereby heating the catalyst bed.
 8. The apparatus of claim 7, whereinsaid vessel means for contacting said deactivated wax-free catalyst withsaid oxidizing gas further comprises a fluidized bed reactor.
 9. Theapparatus of claim 8 further comprising gas distribution meansfunctioning to distribute said oxidizing gas uniformly across a crosssection of said fluidized bed reactor.
 10. The apparatus of claim 9,wherein said gas distribution means further comprises a plate meansfunctioning to support the deactivated wax-free catalyst.
 11. Theapparatus of claim 10, wherein said catalyst bed is maintained at atemperature less than about 250° C.
 12. The apparatus of claim 9,wherein the vessel means used for contacting said deactivated wax-freecatalyst with an oxidizing gas is the same apparatus as the extractionvessel used for extracting wax during the wax extraction process.
 13. Anapparatus useful for contacting an oxidized catalyst with solutioncontaining an alkali metal in the presence of an inert gas to form anoxidized catalyst precursor after a wax extraction process in anextraction vessel, said apparatus comprising: vessel means forcontacting said oxidized catalyst with said alkali metal containingsolution to form a catalyst bed; heating means functioning to heat thevessel means, thereby heating a catalyst bed; and evaporation meansfunctioning to evaporate said alkali metal containing liquid solutionfrom said oxidized catalyst precursor.
 14. The apparatus of claim 13,wherein said vessel means further comprises a three phase bubble columnreactor.
 15. The apparatus of claim 14 further comprising gasdistribution means functioning to distribute a synthesis gas uniformlyacross a cross section of said bubble column reactor.
 16. The apparatusof claim 15, wherein said gas distribution means further comprises asintered metal plate.
 17. The apparatus of claim 14, wherein the vesselmeans used for alkalizing the oxidized catalyst is the same apparatus asthe extraction vessel used for extracting wax during the wax extractionprocess.
 18. The apparatus of claim 14, wherein the evaporation meansused for evaporating alkali metal containing liquid is the sameapparatus as the extraction vessel used for extracting wax during thewax extraction process.
 19. The apparatus of claim 13, wherein saidalkali metal containing liquid solution can be evaporated from saidvessel means by raising the temperature until a dry catalyst powder isproduced.
 20. An apparatus useful for regenerating a deactivatediron-based Fischer-Tropsch catalyst from a slurry bubble column reactor,said apparatus comprising: means functioning to remove wax andimpurities from a deactivated iron-based Fischer-Tropsch catalyst; meansfunctioning to separate a wax-free catalyst from an extraction solventin a wax-free catalyst and solvent bearing solution and to form a drycatalyst powder; means functioning to oxidize said wax-free catalyst toan original Fe₂O₃ catalyst precursor state; means functioning to contactsaid oxidized wax-free catalyst with solution containing an alkali metalin the presence of an inert gas to form an oxidized catalyst precursor;and means functioning to activate said oxide catalyst precursor for usein a FT slurry bubble column reactor.